Method for monitoring the condition of a gear pump of an extracorporeal blood treatment device and extracorporeal blood treatment device

Abstract

Method for monitoring the condition of a gear pump (1) of a device (100) for extracorporeal blood treatment comprising the steps: - Determining a normalization characteristic map, wherein the normalization characteristic map for a new reference gear pump (1) relates a volume flow rate (Q) of a fluid (2) generated by the reference gear pump (1), a pressure (Δp) of the fluid (2) applied to the reference gear pump, a torque (M) generated by the reference gear pump (1) and a rotational speed (n) of the reference gear pump (1) to each other, - during the operation of the gear pump (1), determining an operating characteristic map, wherein the operating characteristic map for a gear pump (1) used during a certain operating period relates a volume flow rate (Q) of the fluid (2) generated by the gear pump (1), a pressure (Δp) of the fluid (2) applied to the gear pump (1), a torque (M) generated by the gear pump (1) and a rotational speed (n) of the gear pump (1) to each other, and - Determining the condition of the gear pump (1) as a function of the normalization map and the operating map.

Description

[0001] The invention is based on the objective of providing a method for monitoring the condition of a gear pump of an extracorporeal blood treatment device and an extracorporeal blood treatment device that enable simple and reliable condition monitoring.

[0002] The method is used to monitor the condition of a gear pump of a specific type in a device for extracorporeal blood treatment, for example in the form of a dialysis machine.

[0003] A gear pump can be, for example, an external gear pump, an internal gear pump, a ring gear pump (also called a gerotor pump or Eaton pump), or a screw pump. For further information, please refer to the relevant technical literature.

[0004] According to the invention, a normalization characteristic map is determined, wherein the normalization characteristic map for a new reference gear pump of the same type mathematically or formulaically relates a fluid volume flow generated by the reference gear pump, a (differential) pressure of the fluid acting on the reference gear pump, a (shaft) torque generated by the reference gear pump or its electric motor, and a rotational speed of the reference gear pump to one another. The torque generated by the reference gear pump is, in particular, the torque acting on the driven gear of the reference gear pump. The rotational speed of the reference gear pump is, in particular, the rotational speed of the driven gear of the reference gear pump. A new gear pump of the device can serve as the reference gear pump. Alternatively, the reference gear pump is a new gear pump whose type corresponds to the type of gear pump of the device.The normalization characteristic map can be determined in advance, for example by the manufacturer of the gear pump, and stored in a memory assigned to the control system of the device.

[0005] During operation of the device's gear pump, an operating characteristic map is determined, whereby the operating characteristic map for the gear pump used during a certain operating period mathematically or formulaically relates the volume flow of the fluid generated by the gear pump, the pressure of the fluid at the gear pump, the torque generated by the gear pump and the speed of the gear pump to each other.

[0006] Finally, the (wear) condition of the device's gear pump is determined as a function of the normalization map and the operating map.

[0007] The condition can be assessed, for example, using the categories "good", "still usable", and "no longer usable". Quantification using a wear indicator with a predefined range of values ​​is also possible, for example, a range between 0 and 10, where a value of 0 describes a defective or completely worn gear pump and a value of 10 describes a new or unused gear pump.

[0008] In one embodiment, the state of the gear pump of the device is determined as a function of a difference between the normalization characteristic map and the operating characteristic map.

[0009] In one embodiment, the normalization characteristic map describes the torque generated by the reference gear pump as a function of the fluid volume flow generated by the reference gear pump, the fluid pressure at the reference gear pump, and the rotational speed of the reference gear pump.

[0010] In one embodiment, the operating characteristic map describes the torque generated by the gear pump of the device as a function of the volume flow of the fluid generated by the gear pump of the device, the pressure of the fluid at the gear pump of the device and the speed of the gear pump of the device.

[0011] In one embodiment, in addition to the condition of the device's gear pump, a prediction of the remaining service life of the device's gear pump is determined as a function of the normalization characteristic curve and the operating characteristic curve. The remaining service life is also referred to as Remaining Useful Life (RUL).

[0012] In one embodiment, the remaining service life of the device's gear pump is calculated using a gear pump-specific regression model. The remaining service life serves, for example, as the regression criterion. The difference between the normalization map and the operating map, for example, serves as the predictor.

[0013] The device according to the invention for extracorporeal blood treatment with a gear pump is designed to carry out a procedure described above.

[0014] The invention is based on the understanding that a difference between the normalization characteristic curve and the operating characteristic curve is characteristic of an (aging) condition or aging of the gear pump, and that a prediction for the remaining service life (RUL) of the gear pump can also be derived from this difference. In principle, an increasing difference reflects a deteriorating condition of the gear pump and suggests a shorter remaining service life.

[0015] The normalization characteristic curve can, for example, be determined by measurement for a given type of gear pump and / or read from a manufacturer's database of the gear pump.

[0016] According to the invention, the degradation of gear pumps is evaluated to predict their remaining service life. The evaluation of the current wear state is based on a change in the characteristic map.

[0017] In general, the efficiency η is defined based on the first law of thermodynamics for gear pumps or positive displacement pumps as follows: η=QΔpPs=QΔp2πMsn

[0018] Here, Q is the delivered volume flow rate, Δp is the pressure increase of the gear pump, M S the (shaft) torque and n the rotational speed. P S describes the wave power.

[0019] This relationship holds true under the assumption of an incompressible pumping fluid and negligible play in the mechanical parts, as well as without heat flow. These assumptions can be considered approximately correct for the pumping fluid in a dialysis machine. The values ​​for Q, Δp, M S , n are measured using associated sensors and stored if necessary.

[0020] First, and especially once, the normalization characteristic M is used. N= f(Q,Δp,n) for a new reference gear pump of a specific type at a defined fluid reference temperature.

[0021] Furthermore, lower limits of an operating characteristic curve M that has changed due to aging are determined, for example experimentally. B determined.

[0022] The normalization characteristic M N and the operating characteristic curve M B describe the (shaft) torque M generated by the gear pump. S depending on the volume flow Q of the fluid generated by the gear pump, the pressure Δp of the fluid at the gear pump and the rotational speed n of the gear pump.

[0023] During operation of the dialysis machine, the operating characteristic curve M is determined. BFirst, the fluid temperature is set to the fluid reference temperature at the dialysis machine. Then, the operating characteristic curve is measured at characteristic, predefined points M. B = f(Q, Δp, n) sampled.

[0024] The operating characteristic curve M determined in this way B is approximated using a suitable function, for example a piecewise linear function or a nonlinear function.

[0025] Age-related wear leads to a change in the operating characteristic curve. The wear or condition of the gear pump can be quantified using a detection function, such as a difference, a squared deviation, etc. This detection function compares the operating characteristic curve with the normalization characteristic curve. The result of this comparison is, for example, a wear indicator that reflects the condition of the gear pump.

[0026] Future wear behavior can be predicted using a machine-specific regression model.

[0027] For example, the wear characteristic of a previously unused gear pump can be determined over time at a constant fluid reference temperature. The determined time-dependent behavior can then be approximated by an nth-order function using conventional mathematical methods.

[0028] To estimate the remaining service life of the gear pump in relation to its function, an instantaneous wear index is determined. Based on this instantaneous wear index and a mathematical inversion of the function, the time at which a predefined threshold is undershot is calculated. The time until this point is reached is, by definition, the remaining service life of the gear pump. The threshold is chosen to accurately represent a typical wear limit. Statistical methods can be used to determine the uncertainty range for the calculated remaining service life.

[0029] The invention is described in detail below with reference to the drawings. These show: Fig. 1. A highly schematic device for extracorporeal blood treatment in the form of a dialysis machine with a gear pump and Fig. 2 a course of a wear indicator of an unused gear pump of Fig. 1 over time.

[0030] Fig. Figure 1 shows in a highly schematic way a device 100 in the form of a dialysis machine with a conventional gear pump 1.

[0031] The condition monitoring of the gear pump 1 is described in detail below.

[0032] First, a normalization characteristic M is generated, particularly once. N = f(Q,Δp,n) for a new reference gear pump 1 of a type corresponding to the type of gear pump 1 of device 100, sampled or determined at defined fluid reference temperature.

[0033] The normalization characteristic M N describes a (shaft) torque M generated by means of a reference gear pump 1a Sdepending on a volume flow rate Q of a fluid 2 generated by means of the reference gear pump 1, a pressure Δp of the fluid 2 at the reference gear pump 1 and a rotational speed n of the reference gear pump 1.

[0034] During the operation of the dialysis machine 100, an operating characteristic curve M is determined. B First, the fluid temperature is set to the fluid reference temperature on the dialysis machine 100. Then, the operating characteristic curve M is set. B at characteristic predefined points M B = f(Q,Ap,n) sampled. The operating characteristic M B describes the (shaft) torque M generated by the gear pump 1 of the dialysis machine 100. Sdepending on the volume flow Q of the fluid 2 generated by the gear pump 1 of the dialysis machine 100, the pressure Δp of the fluid 2 at the gear pump 1 of the dialysis machine 100 and the rotational speed n of the gear pump 1 of the dialysis machine 100.

[0035] Furthermore, lower limits of an operating characteristic curve M that has changed due to aging are determined, for example experimentally. B determined.

[0036] The operating characteristic curve M determined in this way B is approximated using a suitable function, for example a linear function or a nonlinear function.

[0037] Age-related wear leads to a change in the operating characteristic curve M B The wear or condition of the gear pump 1 is quantified using a detection function that, for example, calculates a difference, a squared deviation, etc., between the normalization characteristic curve M. Nand the operating characteristic curve M B The detection function calculates a wear indicator VK, which represents the (wear) condition of the gear pump 1.

[0038] Future wear behavior is predicted using a machine-specific regression model.

[0039] Fig. Figure 2 shows a progression of the wear indicator V K The performance of a previously unused gear pump 1 over time t at a constant fluid reference temperature. The determined time course is approximated by an nth-order function using conventional mathematical methods.

[0040] In order to estimate the remaining service life of the gear pump 1 in conjunction with its function, an instantaneous wear indicator V is first determined. K determined. Then, based on the current wear indicator V, Kand mathematically inverting the function calculates at which time t A the wear indicator V K a threshold value V S The time period until this point in time t A The threshold value V is, by definition, the remaining service life of the gear pump. S The value is chosen to accurately represent a typical wear limit. Statistical methods can be used to calculate an uncertainty range for the remaining service life.

Claims

[1] Method for monitoring the condition of a gear pump (1) of a specific type of device (100) for extracorporeal blood treatment, comprising the steps: - Determining a normalization characteristic curve (M N ), where the normalization characteristic (M N ) relates to each other a volume flow rate (Q) of a fluid (2) generated by means of the reference gear pump (1), a pressure (Δp) of the fluid (2) applied to the reference gear pump (1), a torque (M) generated by means of the reference gear pump (1) and a rotational speed (n) of the reference gear pump (1) for a new reference gear pump (1) of a certain type, - during operation of the gear pump (1), determining an operating characteristic map (M B ), where the operating characteristic curve (M B) relates to each other the volume flow rate (Q) of the fluid (2) generated by the gear pump (1), the pressure (Δp) of the fluid (2) at the gear pump (1), the torque (M) generated by the gear pump (1) and the rotational speed (n) of the gear pump (1) for a specific operating period, and - Determining the condition of the gear pump (1) as a function of the normalization characteristic map (M N ) and the operating characteristic map (M B ). [2] Method according to claim 1, characterized by , that - the state of the gear pump (1) as a function of a difference between the normalization characteristic map (M N ) and the operating characteristic map (M B ) is determined. [3] Method according to any one of the preceding claims, characterized by , that - the normalization map (M N) describes the torque (M) generated by the reference gear pump (1) as a function of the volume flow rate (Q) of the fluid (2) generated by the reference gear pump, the pressure (Δp) of the fluid (2) at the reference gear pump (1) and the rotational speed (n) of the reference gear pump (1). [4] Method according to any one of the preceding claims, characterized by , that - the operating characteristic curve (M B ) describes the torque (M) generated by the gear pump (1) as a function of the volume flow rate (Q) of the fluid (2) generated by the gear pump, the pressure (Δp) of the fluid (2) applied to the gear pump (1) and the rotational speed (n) of the gear pump (1). [5] Method according to any one of the preceding claims, characterized by , that - in addition to the condition of the gear pump (1), a prognosis for the remaining service life of the gear pump (1) depending on the normalization characteristic map (M N) and the operating characteristic map (M B ) is determined. [6] Method according to claim 5, characterized by , that - the remaining service life of the gear pump (1) is calculated using a gear pump-specific regression model. [7] Device (100) for extracorporeal blood treatment with a gear pump (1) configured to perform a method according to one of the preceding claims.

Images